Method for displaying statistically occurring events

ABSTRACT

The invention relates to a method for rapidly and accurately displaying the frequency of statistically occurring events, which method provides a display value after only a short period even in the case of low frequencies. The smoothing required for a high-resolution display when events occur at a low frequency is carried out with relatively little delay. It does not prevent a rapid change to higher display values when the frequency of events rises rapidly. Said method is therefore especially suitable for displaying statistically occurring immission and for traffic monitoring and control.

FIELD OF THE INVENTION

Indication method for statistically occurring events The inventionrelates to a method for indicating the frequency of statisticallyoccurring events and devices for using the method. In the explanationsbelow, the detection of radioactive radiation is assumed as an exampleof statistically occurring events. However, it is pointed out that theinvention is not restricted to the specific kind of statisticallyoccurring events, but rather may also serve, by way of example, forindicating the current traffic density in road traffic or the stream ofvisitors to facilities.

DESCRIPTION OF THE RELATED ART

An array of methods are known which are supposed to make it possible torepresent the frequency of statistically occurring events in ameaningful manner.

Thus, the intensity of radioactive radiation is indicated by measuringdevices with an analog direct-reading instrument by each pulse of thesensor being assigned a specific electric charge and the currentresulting from the rate of charges which corresponds to the sensor pulserate being conducted through the analog direct-reading instrument. Ifthis direct-reading instrument is equipped with a sufficiently longmechanical time constant, then the resultant low-pass filtering producesan indication corresponding to the pulse rate.

The intensity of radioactive radiation is indicated by measuring deviceswith numerical indication by the number of pulses of the sensor beingcounted over a specific duration, for example one minute, and the numberbeing indicated either continually or finally. The measurement time isoften selected such that the indicated number of pulses corresponds tothe rate with a unit selection.

Other devices do not have a time reference, but rather count the pulsescontinually from the beginning of a measurement to the end of ameasurement, in order, for example, to be able to determine the totalradiation load.

The published patent application 30 25 489 describes a device formeasuring ionizing radiation which measures the time duration betweenthe detected radiation pulses. Owing to the statistical behavior ofionizing radiation, the time interval between a plurality of radiationpulses is measured and the corresponding mean value is formed. Theinterval between two determinations of the mean value corresponds to thetime interval between the first and last radiation pulse included in theaveraging. Thus, a new measured value can be determined in a short timeonly at high rates.

U.S. Pat. No. 4,090,082 describes how, by taking account of the deadtime of a Geiger-Müller counter tube, it is possible to improve thelinearity of Geiger-Müller counters toward very high pulse rates and howthe counting of pulses and its indication can expediently be effected.The dead time consideration is negligible or at least of secondaryimportance for Geiger-Müller counter tubes provided for an applicationoutside highly loaded radiation areas. Thus, the dead time in the caseof the known counter tube LND712 is 90 microseconds; the typical pulserate in the case of environmental radioactivity is in the region of lessthan one pulse per second. If, by way of example, motor vehiclestraveling past are used as events to be recorded, then the dead timeconsideration acquires considerable importance owing to the relativelyhigh event rate in that case for many sensors.

U.S. Pat. No. 4,837,705 describes a method for calculating the rate ofchange of the frequency of statistical events. This explains howdifficult it is to ascertain how rapidly the neutron rate in a nuclearreactor is increasing or decreasing, because in order to determine itaccurately, as is necessary for the purpose of controlling andmonitoring nuclear power stations, a long measurement duration isnecessary and also tenable in the case of a low frequency of statisticalevents, while accurate determination is possible rapidly and is alsonecessary in the case of a high frequency.

The methods known to date are affected by many problems which limittheir use or even make them dangerous to use. Thus, although analogmeasuring devices are still suitable for fast indication, they are notsuitable for accurate evaluation or for long-term integration of themeasured radiation. The numerical measuring devices based on countersare not suitable for fast indication of radiation that has increased toa great extent. For this reason, they are often combined with acousticindication, which is intended to inform the observer about the presentintensity of the radiation.

For the purpose of temporally resolved logging, a number of measuringdevices are provided with an analog output which supplies a signal thatcorresponds to the current pulse rate and can be recorded. Onedisadvantage of such logging is that the handling of the measurements ismade more difficult and its evaluation becomes costly and complicated.

SUMMARY OF THE INVENTION

In the case of the methods used in nuclear power stations, the technicaloutlay for determining indication values is of only secondaryimportance. Thus, U.S. Pat. No. 4,837,705 specifies that, by way ofexample, the pulses are in each case counted for a tenth of a second and16,640 such counts are stored and used for determining measured values.

A further problem is that although the measuring devices indicate thecurrent or the averaged rate of the radiation, they do not indicate thepermissible residence duration linked to the indicated rate. Thesensitivity of Geiger-Müller counter tubes used as sensor is usuallyspecified in pulse rate per dose, for example in 1.8 pulses per secondfor each microsievert per hour. This corresponds to 6480 pulses permicrosievert. The permissible annual dose for personnel professionallyexposed to radiation is for example 50 millisievert in Germany, fromwhich the sensor pulse number corresponding to this annual dose can bedetermined in a customary manner, 324,000,000 pulses in the example. Thepermissible residence duration results, as is generally known, from thispulse number referring to a year and divided by the currently measuredpulse rate. Thus, in the example, a pulse rate of about 20 pulses persecond produces a permissible residence duration of half a vear.

The object of the invention is to avoid the disadvantages of the knownmethods and devices and to make it possible that firstly, on the onehand, indication values which are as accurate as possible are displayedas fast as possible and, secondly, the rate and the permissibleresidence duration are indicated.

According to the invention, the above object is achieved by means of amethod according to claim 1. In order to indicate the rate of the pulsesoutput by the sensor, the rate corresponding to the rate of recordedevents, for each individual pulse the current time period is in eachcase defined as a temporal feature and either the latter is stored andthe indication values and their representation are calculated from thestored features or, for each time period, the pulses assigned theretoare counted and these numbers are stored and the indication values andtheir representation are calculated therefrom. For simultaneousgraphical representation of the pulse rate and the permissible residenceduration, a nonlinear, for example a logarithmic, graphical indicationof the pulse rate in a bar with dual scaling, in opposite directions,for the pulse rate and the permissible residence duration is performed.

In one refinement of the invention, the point in time at which the pulseoccurs, for example with a resolution of one second, is determined asthe temporal feature of said pulse and is stored in a circulating memoryhaving a specific number of memory locations. At the respective point intime of a desired indication, the difference between the current timeand the oldest time stored in the circulating memory is formed and thenumber of memory locations is divided by this and indicated as the rate,if appropriate scaled with a factor. Furthermore, the number of pulsesis counted in a counter and stored for logging purposes at intervalswith the current temporal feature.

The position of the oldest time in the circulating memory corresponds tothat at which the temporal feature of the next pulse is to be entered.The essential advantage of this refinement is that even given a lowrate, an indication with indication values having relatively littlevariation is achieved and, if the radiation increases, the indicationimmediately increases and reaches its final steady-state value with ashorter and shorter averaging time.

When a device according to the invention is switched on, the indicatedvalue is incorrect until the circulating buffer has been filled for thefirst time.

In a first further refinement of the invention, therefore, until thecirculating buffer has been completely filled for the first time, theswitch-on point in time is used as the oldest time and the currentnumber of used memory locations is used as the number of memorylocations. This means that the indication initially varies more greatlyowing to the initially smaller number of pulses which contributes to theaveraging.

In a second further refinement of the invention, when the measuringdevice is switched on, in accordance with the expected rate,pre-allocation of the memory locations is carried out with previoustemporal features corresponding to the rate. As a result, the variationof the indication corresponds to steady-state behavior even directlyafter the switch-on.

In one refinement of the invention, a time period whose formation isbased on a clock cycle, for example with a clock period of one second,is selected as the temporal feature of the pulse, and the numbers ofpulses occurring per second are stored in a circulating memory having aspecific number of memory locations. At the respective point in time ofa desired indication, the sum of the numbers stored in the memorylocations is divided by the number of memory locations and indicated asthe rate, if appropriate scaled with a factor. If the number of memorylocations is selected skillfully, for example 64 if binary numbers areused or for example 100 if decimal numbers are used, point shifting issufficient so that explicit division can be dispensed with. Theessential advantage of this refinement is that an indication withindication values having very little variation is achieved at a highrate.

In a further refinement, each pulse is given a consecutive number andthe number of the pulse is stored in the position corresponding to thecurrent time period in the circulating memory. As a result, it is nolonger necessary to calculate the sum of all the numbers stored in thememory locations, but rather only the difference between the currentpulse number and the oldest stored one, which is in the memory positionto be written to next.

In one refinement of the invention, a first circulating memory isallocated the points in time of the pulses, and a second circulatingmemory is allocated the number of pulses per clock cycle. As long as thenumber of pulses in the second circulating memory does not reach orexceed a selected limit value, the rate is determined according to amethod described above, otherwise according to a second of the methodsdescribed above. The effect achieved by this is that the averaging timeis different at a relatively low rate than at a relatively high rate;for example inversely proportional to the pulse rate at a relatively lowrate and constant at a relatively high rate. As a result, a relativelyfast and well smoothed indication is achieved at a relatively low rateand a relative improvement in the smoothing without a disturbing delayin the indication is achieved at a relatively high rate. The limit usedfor changing over between the two methods may be selectable by the userof the method. For many applications, a value corresponding to twice thenatural radiation will be suitable for this purpose. This value may alsobe adaptively incorporated by a device.

The resolution that can be attained for the rate depends on thesensitivity of the sensor and on the averaging time used. In the case ofa logarithmic bar representation, therefore, the indicated bar lengthbecomes smoother and smoother, the greater the rate is. For a numericalindication, an indication resolution corresponding to the averaging timecurrently used in each case is selected in one refinement of theinvention.

The invention makes it possible to read at any time from the length,displayed in the indication, of a single indication bar both the currentrate and the permissible residence duration, for example 2 millisievertsper hour for the rate and 1 day for the permissible residence duration.This applies even directly after the switch-on, without unreasonablevariation of the indication occurring. In this case, a large range canbe displayed appropriately.

If the method according to the invention is realized in a discretesignal processing technology, then it makes suitable signals availablefor the continual logging of pulse rates and total number of pulses withthe assigned reference times.

If a vehicle moving past is regarded as the event to be recorded and aninduction loop, for example, is used as the sensor, then the method canbe applied particularly well in traffic counting for the purpose ofassessing the road traffic density.

Further advantageous refinements emerge from the following descriptionof exemplary embodiments. In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical device for carrying out the method according tothe invention,

FIG. 2 shows a further device for carrying out the method according tothe invention,

FIG. 3 shows a combination of the devices according to FIGS. 1 and 2,

FIG. 4 shows the classification of a display according to the invention,

FIG. 5 shows the representation of a display driven at the maximumlevel,

FIG. 6 shows the representation of a partly driven display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A typical arrangement of a configuration of the invention is illustratedin FIG. 1. The radiation sensor 1 records in a generally known manner astatistically occurring event 19, in the case of radiation, for example,a radiation particle incident on the sensor, and generates, as reportingsignal 2, a pulse reporting the event. This pulse increments the counter3 by one. As a result of the capacity limiting of the counter 3, thelatter is a circulating counter which, when its maximum value Nmax hasbeen exceeded, starts again from the beginning. The content of thecounter 3 forms the address 4 of the memory 5, which has a number ofmemory locations 6 which corresponds to the maximum value Nmax of thecounter 3. By means of an edge of the pulsed reporting signal 2, thecontent of the memory location 6 addressed by the address 4 istransferred to the register 7 and the current time signal 8 of the timer9 is written to the same memory location 6 and to the register 10. Thecontent of the register 7 represents the point in time of the earliestevent 2 still recorded in the memory 5 and is fed as signal 11 to thesubtractor 13; the content of the register 10 represents the point intime of the most recent event 2 yet to be recorded in the memory 5 andis fed as signal 12 to the subtractor 13. The output signal of thesubtractor 13 represents the duration 14 which was necessary for thelast Nmax+1 events 2. From this, the rate signal 16 is formed in thedivider 15 by the division of an optionally selectable constant (notillustrated here) by the duration 14. The rate signal 16 can beindicated directly. It is logarithmized by the logarithm finder 17 withthe assistance of an optionally selectable reference constant (notillustrated here) and displayed as signal 18, preferably on a graphicalpointer-type or bar display, as illustrated in FIGS. 4 to 6.

A further typical arrangement of a configuration of the invention isillustrated in FIG. 2. The sensor 1 records an event 19 and generates,as reporting signal 2, a pulse reporting the event. This pulseincrements the counter 20 by one. The time signal 8 of the timer 9 formsthe address of the memory 21, which has a number of memory locations 22which corresponds to the averaging time, divided by the period of thetimer 9. As a result of a change in the time signal 8, the content ofthe memory location 22 addressed by the time signal 8 is transferred tothe register 24 and the output signal 25 of the counter 20 is written,as the number of the current event 19, to the same memory location 22and to the register 24. The content of the register 24 represents thenumber of the earliest events 19 still recorded in the memory 21 and isfed as signal 27 to the subtractor 28; the content of the register 23represents the number of the most recent events 19 yet to be recorded inthe memory 21 and is fed as signal 26 to the subtractor 28. The outputsignal 29 of the subtractor 28 represents the number of events 19 whichhas been recorded by the sensor 1 during the averaging time and countedby the counter 20, and is thus a rate signal. In a multiplier or divider(not illustrated), the rate signal 29 can be adapted to selectable unitsof measurement with an optionally selectable constant (not illustratedhere). The rate signal 16 can be directly indicated. It is logarithmizedby the logarithm finder 30 with the assistance of an optionallyselectable reference constant (not illustrated here) and displayed assignal 31.

A combination of the two arrangements corresponding to FIG. 1 and FIG. 2is illustrated in FIG. 3. The rate signal 29 is compared with anoptionally selectable limit value (not illustrated) in the limit valuechecker 32. If it exceeds said limit value, then a comparatively highevent rate is present; consequently, the relative statistical variationrange of the rate signal is so small that an accurate indication isachieved by the signal 31 and the latter is selected as indicationsignal 35 by the changeover switch 34 from the two signals 18 and 31. Inthe other case, there are relatively long time intervals between theevents 19 recorded by the sensor 1; the signal 18 corresponds to theaverage rate of the last Nmax recorded events, with the result that thesignal 18 switched to the display in this case by the changeover switch34 affords a minimum accuracy corresponding to Nmax.

A typical configuration of a bar display for simultaneously indicatingthe current rate and the permissible residence duration for this isillustrated in FIGS. 4 to 6, FIG. 4 illustrating the constituent partsof first scale 36, containing permissible residence durations in theexample, second scale 37, exhibiting dose equivalent rates correspondingto a rate in the example, and bar graph 38, consisting of 27 segments inthe example.

FIG. 5 illustrates driving at the maximum level and FIG. 6 illustratespartial driving, which can be read in the context of the bar resolutionfor the rate at “2 mSv/h” and for the permissible residence duration at“1 d”.

The bar illustrated in FIGS. 4 to 6 consists for example of 27 barsegments and the rate inscription consists of customary abbreviationsfor customary rate units “microsievert per hour”, “millisievert perhour” and “sievert per hour”, and the inscription of the permissibleresidence duration consists of customary abbreviations for customarydurations “year”, “ten days”, “day”, “hour” and “six minutes”.

Other rate units, time units, bar resolutions, configurations, forexample in the form of a round scale, also lie within the scope of theinvention. The resolutions and configuration features used in theexample illustrated in FIGS. 2 and 3 are typical of liquid crystaldisplays and vacuum fluorescent displays, where it is often necessary tomanage with as few segments as possible for economical reasons.

The respective reference scale is made recognizable by the lengtheningof individual bar segments. It is also possible to realize said scaleseparately. In the example, the scaling is selected to be logarithmic,with a resolution of four segments per decade. As a result, a range ofalmost seven decades can be appropriately represented with 27 segments.Thus, the display in FIG. 3 [sic] indicates a rate of about 2millisieverts per hour and a permissible residence duration of one day.In parallel, it is possible to represent the exact rate in an additionalnumerical indication which may also be concomitantly included in thesame display element.

List of reference symbols

1 radiation sensor

2 reporting signal

3 counter

4 address of the

5 memory 5

6 memory

7 memory location

8 register

9 time signal

10 timer

11, 12 register signal (point in

13 time of an event)

14 subtractor

15 duration

16 divider

17 rate signal

18 logarithm finder logarithmized rate

19 signal event

20 counter

21 memory

22 memory location

23,24 register

25-27 signal (number of an event)

28 subtractor

29 rate signal

30 logarithm finder

31 logarithmized rate signal

32 limit value checker

33 selection signal

34 changeover switch

35 indication signal

36,37 scale

38 indication bar

39 output value of the memory 5

40 output value of the memory 21

Nmax maximum value of the counter 3

What is claimed is:
 1. Method for indicating the frequency of occurringevents, characterized in that first of all each event is assigned a timeperiod in the form of a time signal as a temporal feature, then thistime signal is stored in a first memory, operated as a circulatingmemory, and a rate signal as an indication value for the rate isdetermined from the respectively stored values by the number of memorylocations of the first memory being divided by the duration as thedifference between the current time signal and the signal correspondingto the oldest time signal stored in the first memory, or, for each timeperiod as time with a uniform time signal, the number of events which isassigned thereto is determined and stored in a second memory, operatedas a circulating memory, and a rate signal as an indication value forthe rate is determined from the respectively stored values by the sum ofthe numbers of events which are stored at the memory locations of thesecond memory being divided by the number of memory locations of thesecond memory.
 2. Method according to claim 1, wherein each event isconsecutively numbered, the respective number of the last of a number ofevents in a time period is determined and stored in the second memoryand a rate signal as an indication value for the rate is determined fromthe respectively stored values by the difference between the number ofthe last event that occurred in the current time period and the numberof an event which is associated with the oldest time period held in thesecond memory being divided by the number of memory locations of thesecond memory.
 3. Method according to claim 1, wherein as a function ofthe number of events stored in the second circulating memory, anoperating mode changeover is performed in which, in the event of aselectable limit value being exceeded for the number of events in thesecond circulating memory, the indication value is determined from therespectively stored values of said second circulating memory, otherwisefrom the stored values of the first circulating memory.
 4. Methodaccording to claim 1, wherein the circulating memories are initiallypreallocated.
 5. Method according to claim 1, wherein the indicationvalue determined corresponds to a rate, said indication value isdeformed nonlinearly, and indicated graphically, the indication havingtwo scalings, the first of which proceeds with the rising indicationvalue and scales an event rate, while the second proceeds in theopposite direction and scales the mean time interval between the eventsor a permissible residence duration.
 6. Apparatus for indicating thefrequency of occurring events, comprising: a) a counter with capacitylimiting is connected to a sensor not belonging to the apparatus; b) thesensor is furthermore connected to a first register and to a secondregister; c) the counter is connected to an address input of a memoryand a timer to a data input of the memory in such a way that an outputsignal of the counter, as an address, selects a memory location whichcan have a time signal of the timer continuously written to it; d) asecond register is likewise connected to the timer; e) the memory has anumber of memory locations corresponding to the maximum value Nmax ofthe counter; f) the content of the addressed memory location of thememory can be transferred to the first register by the reporting signalof the sensor, the time signal of the timer simultaneously being writtento the same memory location and to the register; g) the register isconnected to a subtractor for the purpose of transferring its content,representing the point in time of the earliest event still recorded inthe memory, as the signal, and so is the register, whose contentrepresents the point in time of the most recent event yet to be recordedin the memory; h) a divider is connected to the subtractor, a ratesignal that can be indicated being formed in said divider by division bya constant.
 7. Apparatus according to claim 6, wherein a divider isconnected to the subtractor, a rate signal that can be indicated beingformed in said divider by division by a constant.
 8. Apparatus accordingto claim 7, wherein the constant is freely selectable.
 9. Apparatusaccording to claim 6, wherein a logarithm finder is connected to thedivider.
 10. Apparatus according to claim 9, wherein the logarithmfinder effects logarithm finding with a reference constant. 11.Apparatus according to claim 9, wherein a graphical pointer-type or bardisplay is connected to the logarithm finder.
 12. Apparatus according toclaim 11, wherein the pointer-type or bar display has at least twoscalings, of which at least one identifies an event rate, and another atime interval or a permissible duration.
 13. Apparatus according toclaim 7, in which: a) a first rate signal can be fed to a limit valuechecker; b) an output of the limit value checker is connected to acontrol input of a changeover switch; c) a first of the signal inputs ofthe changeover switch is connected to the output which supplies thefirst rate signal, and a second is connected to the output whichsupplies a second rate signal.
 14. A method for indicating the frequencyof events, comprising the steps of: generating a pulse corresponding toan event; selecting one of counting the number of pulses generated overa time period and correlating a time reference to said generated pulse;calculating the frequency of events based on said selecting; anddisplaying an indication of the frequency of events based on saidcalculated frequency of events, wherein calculating the frequency ofevents based on correlating a time reference to said generated pulseincludes: assigning a time to said generated pulse; storing saidassigned time in a first circulating memory; determining the differencebetween an oldest assigned time stored in said first circulating memoryand the assigned time of said generated pulse; and dividing a number ofmemory locations of said first circulating memory by said determineddifference, and wherein calculating the frequency of events based oncounting the number of pulses generated includes: recording eachgenerated pulse in a second circulating memory; summing the number ofrecorded pulses; and dividing said summed number of recorded pulses by anumber of memory locations of said second circulating memory.
 15. Themethod of claim 14, wherein the selecting step automatically selectscounting the number of pulses generated over a time period if the numberof recorded pulses exceeds a selectable limit.
 16. The method of claim15, wherein the selecting step automatically selects correlating a timereference to said generated pulse if the number of recorded pulses doesnot exceed said selectable limit.
 17. An event frequency counter,comprising: a sensor which generates a pulse corresponding to an event;a timer which generates a time reference; a first circulating memorycoupled to said timer which stores a time reference corresponding toeach generated pulse; a second circulating memory which records theoccurrence of each generated pulse; a selectable calculator whichcalculates the frequency of events; and a display which displays thecalculated frequency of events, wherein said selectable calculator isoperable in a first mode that calculates the frequency of events by:determining the difference between an oldest assigned time stored insaid first circulating memory and the assigned time of a last generatedpulse; and dividing a number of memory locations of said firstcirculating memory by said determined difference, and wherein saidselectable calculator is operable in a second mode that calculates thefrequency of events by: summing the number of recorded pulses; anddividing said summed number of recorded pulses by a number of memorylocations of said second circulating memory.
 18. The apparatus of claim17, wherein the selectable calculator automatically operates in saidfirst mode when said number of recorded pulses does not exceed aselectable limit.
 19. The apparatus of claim 17, wherein said selectablecalculator automatically operates in said second mode when said numberof recorded pulses exceeds a selectable limit.
 20. The apparatus ofclaim 5, wherein the indication value is deformed nonlinearly by beingdeformed logarithmically.